Diverse methods and devices are known from the prior art, with which respective several articles are packed and wrapped respectively to a pack by wrapping with a plastic film and a portion of a plastic film respectively. The packs are liquid containers, for example, being wrapped with a portion of a plastic film, wherein said portion of a plastic film is attached to said pack by heat shrinking process. For example, six PET bottles or glass bottles or cans form a pack with the aid of the plastic film.
The packs for a single pack forming, also referred to as pack type in the following, are generally of the same design and the same size. When changing from one pack type to another pack type, also the design and the size of the packs changes, if necessary. The blanks of a plastic film and the portions of a plastic film respectively have also different dimensions according to the new pack type.
Firstly, the plastic film for the production of the packs is taken, for example, from one or several plastic film provision dispensers of a packing unit, rolls for example, in the form of a continuous film web. Then, the continuous film web is transported via a transport path on the basis of at least partially different rates of feed along further working stations of the packing unit. Finally, the continuous film web is transported to the articles ready to be wrapped and grouped and situated in a film wrapping station of the packing unit. Depending on the design of the packing unit shortly before, during or shortly after the wrapping of the articles with the continuous film web in order to form a pack at the film wrapping station.
Furthermore, it is customary for different pack types that the plastic film of the film wrapping station is supplied with different rates of feed and the grouped articles are wrapped and packed respectively also with different speed. As for packs of the same pack type it may happen, however, that the plastic film of the film wrapping station is also supplied with different rates of feed and the respective grouped articles intended for the packs of the same pack type are wrapped and packed respectively with different speeds. In both cases the rate of feed of the continuous film web has also to follow these changes of the rate of feed at the film wrapping station in areas before the film wrapping station, in order to provide sufficient portions of plastic film for the wrapping process. Per pack it is customary to apply at least one printed image onto the respective portion of a plastic film, which could be a sales message, a label, a brand and/or a bar code, for instance. These printed images are typically designed in the same way for all packs of a pack type and are positioned in the same place onto the respective portion of a plastic film. The printed images of the packs of a pack type differ, for example, in serial numbers or other data.
The printed images can already be applied onto the continuous film web so that different continuous film webs must be provided for different pack types. Alternatively, the printed images are printed onto the continuous film web at a later stage in the packing unit shortly before the articles are packed with a plastic film so that always only one “neutral” not printed continuous film web must be provided independent from the pack type. The printing onto the spread and even continuous film web kept in tension is carried out cleaner and easier than onto the portions of plastic films and/or onto the shrunk plastic film. The printed images are printed in spaced apart printing areas suitable to the size of the packs of the respective pack type onto the continuous film web so that exactly one printed image is positioned at the same position of the pack on the respective portion of a plastic film of the respective pack type which is separated later. In this way, too, a plurality of printed images per portion of a plastic film per pack is producible.
Thus, German patent application DE 10 2006 009 348 A1 discloses a method for the creation of packs consisting of a plurality of packaging units by wrapping said packaging units with a film material. Thereby, the film material is printed with at least one printing unit immediately before the wrapping process, wherein the printing unit is stationary located in direction of travel of the film material between the film supply and the film wrapping station. The feed motion of the continuous film web is controlled at least in the area of the print heads of the printing unit by means of an electronic control unit in order to obtain a definite printed image of high quality.
German patent application DE 22 06 784 A discloses an apparatus for the production of imprints onto single packages wherein said apparatus is positioned at a packing machine of articles. The apparatus has a print roller being stationary mounted on a shaft with at least one sector in which the printing or imprinting elements are stored. The print roller is driven in such a way that it carries out a fraction of a rotation according to a printing sector always in that moment when a printing operation should be carried out. The printing operation is carried out before the articles are packed.
German patent application DE 35 20 499 A1 discloses a packaging machine comprising a forming station for forming containers from a bottom foil, a supply means for supplying a cover foil from a supply rolling over said container, a sealing station for closing the containers with said cover foil, having a drive means for stepwise advancing said bottom and cover foil between the working cycles of said stations and printing means for printing on said cover foil during said working cycles of said stations. A drive means is provided for moving said cover foil through said printing means during said working cycles.
British patent application GB 2 142 282 A discloses an automatic packing machine for articles with a roll, from which a packing sheet is rolled off and transported further to a packing position. A printing unit prints the sheet underneath a receiving roll, wherein a printing tape is drawn out from a tape reel and wound on an empty reel disposed along said packing sheet. A heated type is pressed against the receiving roll through the packing sheet for printing the sheet. The printing process is likewise carried out before the articles are packed with the sheet.
Both, simple and/or small format images and complex and/or large-sized images should be printed onto the continuous film web.